Flat panel display devices are increasingly gaining market acceptance for a variety of different applications. For example, active matrix liquid crystal displays (AMLCD's) have found widespread use as the video monitor in laptop computers, video cameras, and avionic navigation modules, to name a few. Other types of display devices such as electroluminescent (EL) and field emission displays (FED's) are also used in a variety of industrial and consumer settings. The advantage of each of these types of displays resides in the fact that they are all substantially flat. The elements which cause the device to generate an optical effect, whether an AMLCD picture element ("pixel"), or an FED emitter, are sandwiched between two parallel sheets of glass substrates. The spacing between the substrates is critical, and must be uniformly maintained across the entire display face. The spacing between the parallel sheets of glass is on the order of between 1 and about 1,000 .mu.m, depending on the type of display.
Heretofore, uniform spacing has been achieved by the use of spacers disposed between the glass sheets. These spacers have typically taken the form of glass rods, such as optical fibres, or glass spheres, all of the desired size to assure proper spacing. These rods or spheres were then either randomly scattered across the surface of one glass substrate prior to lamination of the second sheet, or randomly dispersed in the display medium, i.e., liquid crystal material, prior to injection between the sealed sheets. This has made for numerous problems impacting on display performance, manufacturing yield, and above all cost of these displays.
Deposition of these spacers has been performed by pre-calculating an initial concentration of spacers for a given area. Thereafter, a reservoir of spacers is positioned above a substrate, and gas is blown into the reservoir, ejecting the spacers. Gravity assures that the spacers fall to the underlying surface, but can do nothing to assure uniform distribution across the substrate, nor their density.
Moreover, this deposition process can do nothing to assure that the spacers do not land on critical circuit elements of the display device. For example, in an AMLCD, a spacer may land upon the pixel current blocking element, i.e., the transistor or diode. This invariably results in either the blocking element being crushed on assembly, or causing a short circuit between the two substrates. In either case, the pixel is inoperative, causing a defect in the display, thus reducing display yield. Alternatively, if the spacer lands upon the pixel electrode, this can contribute to light scattering, and diminished optical performance of the pixel and display. Other problems may result when the spacer conducts heat from the substrate nearest the backlight (in AMLCDs) to the front substrate. These problems are graphically illustrated in FIG. 1, in which a prior art display device is shown. The display device 1, includes first and second display substrates 2, 3, with a current blocking element 4 disposed on the first substrate, and associated with a first electrode 5. A spacer sphere 6 has been dropped on the current blocking element 4, essentially rendering it unusable. This results in a short circuit between the substrates, an inoperative picture element, and localized heating on the viewer proximal side of the display device.
Accordingly, there exists a need for a display device which includes spacers properly located between the glass substrates, in proper densities, and the proper location. The spacers must properly separate the glass substrates, while avoiding contact with the display elements. The display should be fabricated by a process which is readily compatible to the semiconductor processes routinely used in the display fabrication.